1. Field of the Invention
This invention relates to a plug-in package, and more particularly to a data processing device equipped with a plug-in package suitable for safely exchanging a faulty package with a new one in a fault tolerant data processing device.
2. Description of the Related Art
The prior technology for exchange of a plug-in package with another without breaking off the power supply to a data processing device is exemplified by Japanese Patent Publication (KOKOKU) No. 31240/1984, which discloses a concept of connecting a power cable from an external power supply only during the exchange operation, Japanese Patent Laid-Open Publication (KOKAI) No. 108519/1976, which discloses a concept of varying the length of power supply terminals to provide a slight time lag when supplying power to a package, and Japanese Patent Laid-Open Publication (KOKAI) No. 153899/1988, which discloses a concept of causing high-impedance outputs of three-state buffer circuits by utilizing a package removing lever. With the technology disclosed in Japanese Patent Publication No. 31240/1984 and Japanese Patent Laid-Open Publication No. 153899/1988, normal operations cannot be guaranteed when the package is removed without first connecting the power cable or when the package is removed without using the package removing lever. These prior publications do not mention any measures to be taken against any possible misoperation by the operator; a misoperation would damage the package, such as by melting and damaging the power supply terminal portion and would be a cause of noise interference to signals of another package in action. As long as only the technology of Japanese Patent Laid-Open Publication No. 108519/1976 is used, a very reliable package exchange cannot be achieved.